Attributable risks of familial cancer from the Family-Cancer Database.

Population attributable faction (PAF) shows the proportion of the disease that could be prevented if the cause could be removed. PAFs for most types of familial cancer have not been determined. We used the Swedish Family-Cancer Database on 10.2 million individuals and 688,537 parental and 116,741 offspring cancers to calculate familial risks, proportions of affected individuals, and familial PAFs for 28 neoplasms among 0-66-year-old offspring. The data were calculated by an exact proband status in the nuclear families. The familial risks for offspring cancer were increased at 23 of 28 sites from the same cancer in only the parent, at 17 sites from a sibling proband and at 12 sites from a parent and sibling proband. The highest PAFs by parent were for prostate (9.01%), breast (3.67%), and colorectal (5.15%) cancer. However, considering that in gender-specific cancers, the familial effect may originate from grandparents, the PAFs for prostate and breast cancer could be multiplied by 2. The PAFs for the sibling history of prostate, breast, and colorectal cancers were 1.55, 2.85, and 1.23% and for the parent and sibling history 0.99, 0.42, and 0.48%, respectively. Because of mutually exclusive proband definition, the PAFs were additive, giving a total PAF of 20.55% for prostate, 10.61% for breast, and 6.87% for colorectal cancer. The present PAF values give an estimate of the heritable single locus or additive effects for cancer in nuclear families. The data show that the familial PAF of prostate cancer was 20.55%, and breast cancer 10.61%, but for most other sites, it was between 1 and 3%.